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I want to design a tank to hold liquid propane. The proposed tank would have one inlet valve, one output valve, and no sharp edges. I've read that the pressure required to maintain propane in a liquid form at 100 degrees Fahrenheit is 177 psi.

An example analogous to my case; I have a spherical, 40 sq. in. tank in which I want to store liquid propane. If propane must be held at a pressure of 177+ psi to remain in liquid form at 100 degrees Fahrenheit, then the tank must be able to withstand 177 psi * 40 sq. in. = 7080 lbs at all points of the tank's surface. What material properties should I look at to find a material suitable to withstand that force? I want to think tensile strength, but would like an expert's advice.

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    $\begingroup$ For material consider internal and external corrosion, where it is stored etc As for the calculations these two links should point you in the right direction : engineersedge.com/pressure_vessels_menu.shtml and : en.wikipedia.org/wiki/Cylinder_stress. You will also need to be very good at welding.... So, why don't you choose a tank that is pre-made - they come in many shapes and sizes from small and portable to large already designed to meet the relevant codes. $\endgroup$ – Solar Mike Jun 11 '17 at 7:21
  • $\begingroup$ @SolarMike is exactly right. You can buy a code-approved tank in almost any size at your local hardware store. This will be much cheaper and easier than making one, and eliminates any concerns about picking the wrong material or making a design or fabrication error. Making your own propane tank creates nothing but liability. $\endgroup$ – Mark Jun 11 '17 at 12:49
  • $\begingroup$ I appreciate your responses; the tank's purpose is to hold propane, or a mixture of propane and silicone ("green gas") for use as a propellant in toy guns. That being said, it has to fit within the toy gun's magazine, so I cannot use a typical propane tank. I wish to design a tank for this application, so that I may push a design or design requirements out to a dedicated tank manufacturer. $\endgroup$ – Nathan Jun 11 '17 at 17:25
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    $\begingroup$ What about those co2 cartridges - small, threaded or not, recyclable as made of steel? $\endgroup$ – Solar Mike Jun 11 '17 at 22:24
  • $\begingroup$ what does it mean for a sphere to be 40 square inches? $\endgroup$ – agentp Jun 13 '17 at 19:54
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The main material property that determines the bursting strength of a pressure tank is the tensile strength (the stress at the yield point) of that material. Knowing the tensile strength allows you to specify the required wall thickness to withstand the maximum design pressure inside the tank.

Because the amount of energy stored in a pressure tank is large, the amount of damage that can be done by a tank when it bursts is very great. For this reason, pressure tanks are designed to have large factors of safety and in commercial settings their design is highly regulated by safety codes that are established by (for example) the American Society For Testing And Materials, or ASTM.

This in turn means that pressure tank design is not a DIY enterprise. Your legal exposure is severe if a pressure tank you designed from scratch blew up and was not ASTM compliant; in fact, your insurance company will not write you a liability policy unless your pressure vessels are provably built "to code" or purchased from an ASTM-compliant manufacturer.

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